Magnetic Field in plane 90 degrees off Helmholtz coil axis?

[BrickHowes]

In a recent Physics lab, I experimented with the magnetic field generated by two Helmholts coils. I used a Hall probe, and some software created by the Grad students to plot the field strength against probe position in a series of configurations.

I understood almost all of the lab, I understand the field behavior for different separations between coils ON AXIS of the coils.

Here is what I what I do not understand, and I am hoping someone can help me figure it out:

Configuration:
Two Helmholtz coils, separated by the radius of the coil such that the on axis magnetic field is uniform between the coils, and nearly zero outside of the coils.

The probe is brought to the system (configured for radial measurements) such that the tip passes through the plane between the two rings, parallel to their diameters, and perpendicular to their axis. The probe is brought all the way through such that it begins and ends outside of the magnetic field, and experiences zero field at the begging and end of the measurement. The plot of the field strength reveals that the field between the rings is everywhere uniform, and is zero well outside of the rings. Fine, here's what confuses me,

Just as the probe enters or exits the rings, the field shoots negative.
What is a negative magnetic field, and why does it exist at the edges of the helmholtz rings?

Hope i made this clear enough, thank you for any direction...

 

[Hesch]

All magnetic fields are circulating fields. All curves describing direction of the field must return into themselves, so the field does not "shoot negative", it just changes direction outside the helmholz rings:

https://www.google.com/search?q=hel...kipedia.org%2Fwiki%2FHelmholtz_coil;2000;1818

 

[BrickHowes]

Excellent, that helps so much.

Thank you!